Autodeposition metal dip coating process

ABSTRACT

What is disclosed is a no-rinse autodeposition process to dip-apply a metal part in an aqueous resin coating bath with an immersion time and, wherein the removal rate of the dipped part is kept equal or below drainage rate of mobile liquid portion, such that upon removal of the part, drip edge formation is minimized and a DFT is maintained within acceptable tolerance levels.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to dip-application of aqueousautodepositable compositions.

BACKGROUND OF THE INVENTION

[0002] Autodeposition is an aqueous process for coating metal that isdriven by reactions between the coating and metal substrate when smallamounts of multivalent metal ions are released from the metal surface.The aqueous composition must contain a stabilized polymer dispersion.The essential feature of an autodepositable coating is that thedispersed material is stabilized by functional groups on the polymerand/or provided by surface active agents which are sensitive tomultivalent ions entering the aqueous phase. Deposition occurs byinteraction of the multivalent ions and these stabilizing functionalgroups causing the dispersion to precipitate when sufficientconcentration of multivalent ions occurs at the metal surface.

[0003] Examples of autodepositing compositions are disclosed, forexample, in European Patent Publication 0132828, Bashir M. Ahmed, U.S.Pat. No. 4,647,480 and Wilbur S. Hall, U.S. Pat. No. 4,186,219, U.S.Pat. No. 4,657,788, U.S. Pat. Nos. 5,691,048, and 4,657,788, and patentscited therein each of which is incorporated herein by reference. Suchcompositions designed to particularly effective when the resin materialis provided in the form of a dispersed polymer such as asulfonate-functionalized novolak, or latex made from the emulsionpolymerized product of at least two polymerizable ethylenicallyunsaturated monomers.

[0004] In the practice of dip-applied autodeposition coatings, often thecoating can be rinsed after withdrawal from the bath. In some instances,rinsing is not undertaken. There remains some limits on the process ofautodepositing coatings on metal parts without a rinse step. A problemarises without a rinse step relating to accumulation of drainage alongedges, that when dried leads to what is referred to as drip edges. Thesedrip edges result in poorer protective coatings. In attempts toalieviate drip edges other problems can arise, such as variable dry filmthickness (DFT) in different areas of the part surface. The need for anon-rinsing coating method that deposits a sufficient amount of coating,with an acceptable DFT uniformity, while reducing the incidence of dripedges would be highly desirable in a dip-applied autodeposited coating.

SUMMARY OF THE INVENTION

[0005] According to a preferred aspect of present invention there isprovided a no-rinse autodeposition process to dip-apply a metal part inan aqueous coating bath containing a specified solids level, at aspecified bath temperature, immersion time and, wherein the removal rateof the dipped part is kept equal or below drainage rate of mobile liquidportion, such that upon removal of the part, drip edge formation isminimized and a DFT is maintained within acceptable tolerance levels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] Unless otherwise indicated, description of components in chemicalnomenclature refers to the components at the time of addition to anycombination specified in the description, but does not necessarilypreclude chemical interactions among the components of a mixture oncemixed.

[0007] As used herein the term “autodeposited resin” shall mean allresins which can be autodeposited in the autodeposition process.

[0008] DFT is dry film thickness, and is measured using a FisherscopeMMS Permascope and an average of 10 readings are taken as thestatistical sample on each part or panel.

[0009] “Primer” means a liquid composition applied to a surface as anundercoat beneath a subsequently-applied covercoat. The covercoat can bean adhesive and the primer/adhesive covercoat forms an adhesive systemfor bonding two substrates together.

[0010] “Coating” means a liquid composition applied to a surface to forma protective and/or aesthetically pleasing coating on the surface.

[0011] “Electrochemically active metals” means iron and all metals andalloys more active than hydrogen in the electromotive series. Examplesof electrochemically active metal surfaces include zinc, iron, aluminumand cold-rolled, polished, pickled, hot-rolled and galvanized steel.

[0012] “Ferrous” means iron and alloys of iron.

[0013] The autodeposited coatings are resin-containing acidic-aqueouscompositions comprising an acid, an oxidizing agent and the aqueousdispersed resin. Examples of autodeposited compositions are known. Thosewhich are suitable in the present invention are made as set forth inEuropean Patent Publication 0132828 and U.S. Pat. Nos. 4,647,480 and4,186,219.

[0014] The addition polymerized resins which can be autodepositedgenerally comprise at least one ethylenically unsaturated monomericcompound (e.g. vinyl-based resins). The preferred ethylenicallyunsaturated monomers include styrene-butadiene; acrylate;alkyl-substituted acrylates such as methyl methacrylate and ethylmethacrylate; vinyl halides such as vinyl chloride; vinylidene halidessuch as vinylidene chloride and vinylidene dichloride; alkylenes such asethylene; halide-substituted alkylenes such as tetrafluoroethylene; andacrylonitriles such as acrylonitrile, combinations thereof and the like.

[0015] Of the condensation type resins suitable herein are aqueousdispersions of modified phenolic novolak resins. These are the reactionproduct of a phenolic resin precursor, a modifying agent and amulti-hydroxy phenolic compound. The modifying agent includes at leastone functional moiety that enables the modifying agent to react with thephenolic resin precursor and at least one ionic moiety. According to apreferred embodiment the modifying agent is an aromatic compound.According to another embodiment the ionic moiety of the modifying agentis sulfate, sulfonate, sulfinate, sulfenate or oxysulfonate and thedispersed phenolic resin reaction product has a carbon/sulfur atom ratioof 20:1 to 200:1.

[0016] The acid can be any acid that is capable of reacting with a metalto generate a sufficient concentration of multivalent ions. The acidswhich may be used in the autodepositing composition include inorganicand strong organic acids, such as, for example, hydrofluoric acid,hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, aceticacid, halogen—substituted acetic acid such as chloroacetic acid andtrichloroacetic acid, and citric acid. Hydrofluoric acid is a preferredacid used in conjunction with emulsion polymerized autodeposited resins.Phosphoric acid is a preferred acid used in conjunction with modifiedphenolic dispersion embodiments In the case of steel the multivalentions liberated from the metal surface are ferric and/or ferrous ions.When the acid is mixed into the composition presumably the respectiveions are formed and exist as independent species in addition to thepresence of the free acid. In other words, in the case of phosphoricacid, phosphate ions and free phosphoric acid co-exist in the coatingbath. As for modified phenolic dispersion embodiments, the acidpreferably is present in an amount of 5 to 300 parts by weight, morepreferably 10 to 160 parts by weight, based on 100 parts by weight ofthe resin dispersion.

[0017] The oxidizing agents which can be employed in an autodepositingcomposition for use in the present invention include peroxides such ashydrogen peroxide, chromates and dichromates such as chromic acid andpotassium dichromate, nitrates such as nitric acid and sodium nitrate,persulfates such as sodium persulfate and ammonium persulfate,perborates such as sodium perborate, iron (III) such as ferric fluoride.Hydrogen peroxide and ferric fluoride are the preferred oxidizingagents.

[0018] Exemplary autodepositing compositions for use in the presentinvention are those where the resin is in the form of a latex (i.e. anemulsion polymerization product of at least one polymerizableethylenically unsaturated monomer). Examples of such compositionsinclude Autophoretic® 800 Series autodepositing compositions based onpolyvinylidene resins and Autophoretic® 700 Series autodepositingcompositions based on acrylic resins, each composition being made byHenkel. Such compositions preferably contain hydrofluoric acid andhydrogen peroxide or iron (III) fluoride as the oxidizing agent. Othercommercially available autodepositable coatings are provided by LordCorporation under the Autoseal trademark, e.g., MJ 2110 is mostpreferred, and is disclosed in copending application Ser. No. 09/235,201, hereby incorporated by reference. Prior to applying a dip-appliedautodeposition coating, the most preferred metal treatment is providedby the use of an aqueous metal treatment primer composition disclosed incopending application Ser. No. 09/235,778 which is hereby incorporatedby reference.

[0019] The coatings produced by autodepositing compounds underautodepositing conditions generally have an average nominal thickness offrom 0.5 to 3 mils, preferably from about 1.0 to 2.0 mils, applied overa metal treatment having a thickness of from 0.1 to 0.5 mils ±0.05 mils.Water, preferably deionized water, is utilized to establish thepredetermined solids content. Although the solids content may be variedas desired, the solids content of the coating bath is in a range of from3 to 10%. The bath composition is waterborne and substantially free ofvolatile organic compounds. In the practice of the invention the rangeof the average DFT of autodeposited coating over the part surface iskept within ±0.3 mils, preferably +/- 0.2 mils, by processing a totalsolids bath in a range of solids of from 5 wt. % to 10%, preferably 6wt. % solids, at a bath temperature of from 15° C. to 40° C., anImmersion time of from 20 to 80 seconds, preferably from 30 to 75seconds, and a part withdrawal rate of from 1 to 10 ft./minute,preferably from 3 to 6 ft./min.

[0020] In a preferred embodiment of dip-applied method to coat a metalpart an aqueous autodeposition bath comprises a phenolic resindispersion, particularly an aqueous novolak dispersion and a depositioncontrol agent and an optional a flexibilizer component in admixturetherewith..

[0021] This rate of autodeposition is independent of the withdrawal rateof the part. Typically the instantaneous rate of deposition slows withthe elapsed immersion time. This reduction in deposition rate isreferred to as “a self-limiting” feature, however to immersion time islimited to maintain an optimal DFT. Even with the formation of a gelleddeposit on the immersed part, there are components of the autodepositionsystem that further drain from the gel as the part is withdrawn. Thewithdrawal rate is kept at or below the drainage rate in the practice ofthe invention, such that upon complete withdrawal, drip edges arereduced and most preferably eliminated. The standard deviation of DFTmeasured at 10 points on the surface of the part is kept to within 0.05mils to 0.16 mils despite the slow withdrawal rates.

[0022] In the most preferred embodiment, the coating when dried is athin, tightly bound interpenetrating organic/inorganic matrix ofphenolic/metal phosphates at the metal substrate interface. This matrixcan be further flexibilized with polymers. The flexibilizer is anymaterial that contributes flexibility and/or toughness to the filmformed from the composition. The toughness provided by the flexibilizerprovides fracture resistance to the film. The flexibilizer should benon-glassy at ambient temperature and be an aqueous emulsion latex oraqueous dispersion that is compatible with the phenolic novolak resindispersion. The flexibilizer preferably is formulated into thecomposition in the form of an aqueous emulsion latex or aqueousdispersion.

[0023] Suitable resin dispersions include aqueous latices, emulsions ordispersions of (poly)butadiene, neoprene, styrene-butadiene rubber,acrylonitrile-butadiene rubber (also known as nitrile rubber),halogenated polyolefin, acrylic polymer, urethane polymer,ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymerrubber, styrene-acrylic copolymer, polyamide, poly(vinyl acetate) andthe like. Halogenated polyolefins, nitrile rubbers and styrene-acryliccopolymers are preferred.

[0024] A suitable styrene-acrylic polymer latex is commerciallyavailable from Goodyear Tire & Rubber under the trade designationPLIOTEC and described, for example, in U.S. Pat. No. 4,968,741;5,122,566 and 5,616,635. According to U.S. Pat. No. 5,616,635, such acopolymer latex is made from 45-85 weight percent vinyl aromaticmonomers, 15-50 weight percent of at least one alkyl acrylate monomerand 1-6 weight percent unsaturated carbonyl compound. Styrene is thepreferred vinyl aromatic monomer, butyl acrylate is the preferredacrylate monomer and acrylic acid and methacrylic acid are the preferredunsaturated carbonyl compound. The mixture for making the latex alsoincludes at least one phosphate ester surfactant, at least onewater-insoluble nonionic surface active agent and at least one freeradical initiator.

[0025] Nitrile rubber emulsion latex is generally made from at least onemonomer of acrylonitrile or an alkyl derivative thereof and at least onemonomer of a conjugated diene, preferably butadiene. According to U.S.Pat. No. 4,920,176 the acrylonitrile or alkyl derivative monomer shouldbe present in an amount of 0 or 1 to 50 percent by weight based on thetotal weight of the monomers. The conjugated diene monomer should bepresent in an amount of 50 percent to 99 percent by weight based on thetotal weight of the monomers. The nitrile rubbers can also optionallyinclude various co-monomers such as acrylic acid or various estersthereof, dicarboxylic acids or combinations thereof. The polymerizationof the monomers typically is initiated via free radical catalysts.Anionic surfactants typically are also added. A suitable nitrile rubberlatex is available from B. F. Goodrich under the HYCAR® mark.Representative halogenated polyolefins include chlorinated naturalrubber, chlorine- and bromine-containing synthetic rubbers includingpolychloroprene, chlorinated polychloroprene, chlorinated polybutadiene,hexachloropentadiene, butadiene/halogenated cyclic conjugated dieneadducts, chlorinated butadiene styrene copolymers, chlorinated ethylenepropylene copolymers and ethylene/propylene/non-conjugated dieneterpolymers, chlorinated polyethylene, chlorosulfonated polyethylene,poly(2,3-dichloro-1,3-butadiene), brominatedpoly(2,3-dichloro-1,3-butadiene), copolymers of (c-haloacrylonitrilesand 2,3-dichloro-1,3-butadiene, chlorinated poly(vinyl chloride) and thelike including mixtures of such halogen-containing elastomers.

[0026] Latices of the halogenated polyolefin can be prepared accordingto methods known in the art such as by dissolving the halogenatedpolyolefin in a solvent and adding a surfactant to the resultingsolution. Water can then be added to the solution under high shear toemulsify the polymer. The solvent is then stripped to obtain a latex.The latex can also be prepared by emulsion polymerization of thehalogenated ethylenically unsaturated monomers.

[0027] Butadiene latices are particularly preferred as the flexibilizer.Methods for making butadiene latices are widely available commercially,and are described, for example, in U.S. Pat. Nos. 4,054,547 and3,920,600, both incorporated herein by reference. In addition, U.S. Pat.Nos. 5,200,459; 5,300,555; and 5,496,884 disclose emulsionpolymerization of butadiene monomers in the presence of polyvinylalcohol and a co-solvent such as an organic alcohol or a glycol.

[0028] The butadiene monomers useful for preparing a butadiene polymerlatex as a flexibilizer, can essentially be any monomer containingconjugated unsaturation. Typical monomers include2,3-dichloro-1,3-butadiene; 1,3-butadiene; 2,3-dibromo-1,3-butadieneisoprene; isoprene; 2,3-dimethylbutadiene; chloroprene; bromoprene;2,3-dibromo-1,3-butadiene; 1,1,2-trichlorobutadiene; cyanoprene;hexachlorobutadiene; and combinations thereof.

[0029] It is particularly preferred to use 2,3-dichloro-1,3-butadienesince a polymer that contains as its major portion2,3-dichloro-1,3-butadiene monomer units has been found to beparticularly useful in adhesive applications due to the excellentbonding ability and barrier properties of the2,3-dichloro-1,3-butadiene-based polymers. As described above, anespecially preferred embodiment of the present invention is one whereinthe butadiene polymer includes at least 60 weight percent, preferably atleast 70 weight percent, 2,3-dichloro-1,3-butadiene monomer units.

[0030] The butadiene monomer can be copolymerized with other monomers.Such copolymerizable monomers include α-haloacrylonitriles such asα-bromoacrylonitrile and α-chloroacrylonitrile; α,β-unsaturatedcarboxylic acids such as acrylic, methacrylic, 2-ethylacrylic,2-propylacrylic, 2-butylacrylic and itaconic acids;alkyl-2-haloacrylates such as ethyl-2-chloroacrylate andethyl-2-bromoacrylate; α-bromovinylketone; vinylidene chloride; vinyltoluenes; vinylnaphthalenes; vinyl ethers, esters and ketones such asmethyl vinyl ether, vinyl acetate and methyl vinyl ketone; estersamides, and nitriles of acrylic and methacrylic acids such as ethylacrylate, methyl methacrylate, glycidyl acrylate, methacrylamide andacrylonitrile; and combinations of such monomers. The copolymerizablemonomers, if utilized, are preferably α-haloacrylonitrile and/orα,β-unsaturated carboxylic acids. The copolymerizable monomers may beutilized in an amount of 0.1 to 30 weight percent, based on the weightof the total monomers utilized to form the butadiene polymer.

[0031] In carrying out the emulsion polymerization to produce the latex,conventional anionic and/or nonionic surfactants may be utilized inorder to aid in the formation of the latex. Typical anionic surfactantsinclude carboxylates such as fatty acid soaps from lauric, stearic, andoleic acid; acyl derivatives of sarcosine such as methyl glycine;sulfates such as sodium lauryl sulfate; sulfated natural oils and esterssuch as Turkey Red Oil; alkyl aryl polyether sulfates; alkali alkylsulfates; ethoxylated aryl sulfonic acid salts; alkyl aryl polyethersulfonates; isopropyl naphthalene sulfonates; sulfosuccinates; phosphateesters such as short chain fatty alcohol partial esters of complexphosphates; and orthophosphate esters of polyethoxylated fatty alcohols.Typical nonionic surfactants include ethoxylated (ethylene oxide)derivatives such as ethoxylated alkyl aryl derivatives; mono- andpolyhydric alcohols; ethylene oxide/propylene oxide block copolymers;esters such as glyceryl monostearate; products of the dehydration ofsorbitol such as sorbitan monostearate and polyethylene oxide sorbitanmonolaurate; amines; lauric acid; and isopropenyl halide. A conventionalsurfactant, if utilized, is employed in an amount of 0.01 to 5 parts,preferably 0.1 to 2 parts, per 100 parts by weight of total monomersutilized to form the butadiene polymer.

[0032] The preferred dichlorobutadiene homopolymers have a colloidalstabilizing system characterized by anionic surfactants. Such anionicsurfactants include alkyl sulfonates and alkyl aryl sulfonates(commercially available from Stepan under the trade designationPOLYSTEP) and sulfonic acids or salts of alkylated diphenyl oxide (forexample, didodecyl diphenyleneoxide disulfonate or dihexyl diphenyloxidedisulfonate commercially available from Dow Chemical Co. under the tradedesignation DOWFAX).

[0033] Especially preferred butadiene latexes as flexibilizers arepolymerized in the presence of a styrene sulfonic acid, styrenesulfonate, poly(styrene sulfonic acid), or poly(styrene sulfonate)stabilizer to form the latex. Poly(styrene sulfonate) is the preferredstabilizer. This stabilization system is particularly effective for abutadiene polymer that is derived from at least 60 weight percentdichlorobutadiene monomer, based on the amount of total monomers used toform the butadiene polymer. The butadiene polymer latex can be made byknown emulsion polymerization techniques that involve polymerizing thebutadiene monomer (and copolymerizable monomer, if present) in thepresence of water and the styrene sulfonic acid, styrene sulfonate,poly(styrene sulfonic acid), or poly(styrene sulfonate) stabilizer. Thesulfonates can be salts of any cationic groups such as sodium, potassiumor quaternary ammonium. Sodium styrene sulfonate is a preferred styrenesulfonate compound. Poly(styrene sulfonate) polymers includepoly(styrene sulfonate) homopolymer and poly(styrene sulfonate)copolymers such as those with maleic anhydride. Sodium salts ofpoly(styrene sulfonate) are particularly preferred and are commerciallyavailable from National Starch under the trade designation VERSA TL. Thepoly(styrene sulfonate) can have a weight average molecular weight from5×10⁴ to 1.5×10⁶, with 1.5×10⁵ to 2.5×10⁵ being preferred. In the caseof a poly(styrene sulfonate) or poly(styrene sulfonic acid) it isimportant to recognize that the emulsion polymerization takes place inthe presence of the pre-formed polymer. In other words, the butadienemonomer is contacted with the pre-formed poly(styrene sulfonate) orpoly(styrene sulfonic acid). The stabilizer preferably is present in anamount of 0.1 to 10 parts, preferably 1 to 5 parts, per 100 parts byweight of total monomers utilized to form the butadiene polymer.

[0034] The flexibilizer, if present, preferably is included in thecomposition in an amount of 5 parts by weight to 300 parts by weight,based on 100 parts by weight of the preferred phenolic novolak resindispersion. More preferably, the flexibilizer is present in an amount of25 parts by weight to 100 parts by weight, based on 100 parts by weightof the phenolic novolak resin dispersion.

[0035] The modified phenolic resin dispersion can be cured to form ahighly crosslinked thermoset via known curing methods for phenolicresins. The curing mechanism can vary depending upon the use and form ofthe phenolic resin dispersion. For example, curing of the dispersedresole embodiment typically can be accomplished by subjecting thephenolic resin dispersion to heat. Curing of the dispersed novolakembodiment typically can be accomplished by addition of an aldehydedonor compound.

[0036] Since the dispersed phenolic resin is a novolak, a curativeshould be introduced in order to cure the film formed by the metaltreatment composition. It should be noted that the metal treatmentcomposition cannot itself include a phenolic resin curative as thesecuratives are not storage stable under acidic conditions. Curing of thefilm can be accomplished by the application of a curative-containingtopcoat over the metal treatment film. Typically, the metal treatmentcomposition is applied to a metal surface (either conventionally or viaautodeposition) and then dried. The curative-containing autodepositedtopcoat then is applied to the thus treated metal surface. The curativecontained in the topcoat can be an aldehyde donor compound or anaromatic nitroso compound. Topcoat compositions that include either oneor both of these curatives are well-known and commercially available.

[0037] The aldehyde donor can be essentially be any type of aldehydeknown to react with hydroxy aromatic compounds to form cured orcrosslinked novolak phenolic resins. Typical compounds useful as analdehyde (e.g., formaldehyde) source in the present invention includeformaldehyde and aqueous solutions of formaldehyde, such as formalin;acetaldehyde; propionaldehyde; isobutyraldehyde; 2-ethylhexaldehyde;2-methylpentaldehyde; 2-ethylhexaldehyde; benzaldehyde; as well ascompounds which decompose to formaldehyde, such as paraformaldehyde,trioxane, furfural, hexamethylenetetramine, anhydromaldehydeaniline,ethylene diamine formaldehyde; acetals which liberate formaldehyde onheating; methylol derivatives of urea and formaldehyde; methylolphenolic compounds; and the like.

[0038] It has been found that metal parts pre-primer coated with aprimer described in U.S. Ser. No. 09/235,778, formaldehyde speciesgenerated from the resole present in the primer appear to co-cure thenovolak in the metal treatment coating via diffusion. In addition,curing or crosslinking of the novolak may occur through ioniccrosslinking and chelation with the metal ions generated by theacid-metal substrate reaction.

[0039] Additionally, high molecular weight aldehyde homopolymers andcopolymers can be employed as a latent formaldehyde source in thepractice of the present invention. A latent formaldehyde source hereinrefers to a formaldehyde source which will release formaldehyde only inthe presence of heat such as the heat applied during the curing of anadhesive system. Typical high molecular weight aldehyde homopolymers andcopolymers include (1) acetal homopolymers, (2) acetal copolymers, (3)gamma-polyoxy-methylene ethers having the characteristic structure:

R₁₀O—(CH₂O)_(n)—R₁₁

[0040] and (4) polyoxymethylene glycols having the characteristicstructure:

HO—(R₁₂O)_(x)—(CH₂O)_(n)—(R₁₃O)_(x)—H

[0041] wherein R₁₀ and R₁₁ can be the same or different and each is analkyl group having from about 1 to 8, preferably 1 to 4, carbon atoms,R₁₂ and R₁₃ can be the same or different and each is an alkylene grouphaving from 2 to 12, preferably 2 to 8, carbon atoms; n is greater than100, and is preferably in the range from about 200 to about 2000; and xis in the range from about 0 to 8, preferably 1 to 4, with at least onex being equal to at least 1. The high molecular weight aldehydehomopolymers and copolymers are further characterized by a melting pointof at least 75° C., i.e. they are substantially inert with respect tothe phenolic system until heat activated; and by being substantiallycompletely insoluble in water at a temperature below the melting point.The acetal homopolymers and acetal copolymers are well-known articles ofcommerce. The polyoxymethylene materials are also well known and can bereadily synthesized by the reaction of monoalcohols having from 1 to 8carbon atoms or dihydroxy glycols and ether glycols withpolyoxymethylene glycols in the presence of an acidic catalyst. Arepresentative method of preparing these crosslinking agents isdescribed in U.S. Pat. No. 2,512,950, which is incorporated herein byreference. Gamma-polyoxymethylene ethers are generally preferred sourcesof latent formaldehyde and a particularly preferred latent formaldehydesource for use in the practice of the invention is 2-polyoxymethylenedimethyl ether.

[0042] The aromatic nitroso compound can be any aromatic hydrocarbon,such as benzenes, naphthalenes, anthracenes, biphenyls, and the like,containing at least two nitroso groups attached directly to non-adjacentring carbon atoms. Such aromatic nitroso compounds are described, forexample, in U.S. Pat. No. 3,258,388; U.S. Pat. No. 4,119,587 and U.S.Pat. No. 5,496,884.

[0043] The control agent mentioned above is especially useful in themetal treatment composition of the invention described above but itcould also be useful in any multi-component composition that includes anautodepositable component. The autodepositable component is any materialthat enables (either by itself or in combination with the othercomponents of the composition) the multi-component composition toautodeposit on a metal surface. Preferably, the autodepositablecomponent is any water-dispersed or water soluble resin that is capableof providing autodeposition ability to the composition. It is believedthat the present invention will be used most widely in connection withcoatings formed from organic polymers in particular, those polymersderived from ethylenically unsaturated compounds. Other organic polymersuseful in the instant invention are those that can be obtained in a formsuitable for compounding into an aqueous coating bath. Organic resinsinclude those derived from ethylenically unsaturated monomers such aspolyvinylidene chloride, polyvinyl chloride, polyethylene, acrylic,acrylonitrile, polyvinyl acetate and styrene-butadiene (see U.S. Pat.Nos. 4,414,350; 4,994,521; and 5,427,863; and PCT Published PatentApplication No. WO 93/15154). Urethane and polyester resins are alsomentioned as being useful. Certain epoxy and epoxy-acrylate resins arealso said to be useful autodeposition resins (see U.S. Pat. No.5,500,460 and PCT Published Patent Application No. WO 97/07163). Blendsof these resins may also be used.

[0044] The preferred autodepositable resins are aqueous phenolic resindispersions described in co-pending, commonly assigned U.S. patentapplication Ser. No. 09/235,201, incorporated herein by reference. Thenovolak version of this dispersed resin is described above in connectionwith the metal treatment composition. There is also a resole versionwith which the control agent of the invention may be formulated into amulti-component composition.

[0045] The phenolic resin precursor and modifying agent used to make thedispersed resole are the same as those described for the dispersednovolak. However, the dispersed resole is produced by the reaction of 1mol of modifying agent(s) with 1 to 20 mol of phenolic resinprecursor(s). A dispersed resole typically can be obtained by reacting aresole precursor or a mixture of resole precursors with the modifyingagent or a mixture of agents without any other reactants, additives orcatalysts. However, other reactants, additives or catalysts can be usedas desired. Multi-hydroxy phenolic compound(s) can optionally beincluded in relatively small amounts in the reactant mixture for theresole. Synthesis of the resole does not require an acid catalyst.

[0046] Hydrophilic resoles typically have a F/P ratio of at least 1.0.According to the invention, hydrophilic resoles having a F/P ratio muchgreater than 1.0 can be successfully dispersed. For example, it ispossible to make an aqueous dispersion of hydrophilic resoles having aF/P ratio of at least 2 and approaching 3, which is the theoretical F/Pratio limit.

[0047] According to a particularly preferred embodiment disclosed inU.S. Ser. No. 09/235,201, wherein the dispersed phenolic resin is aresole and the modifying agent is a naphthalene having a ionic pendantgroup X and two reaction-enabling substituents Y, the dispersed phenolicresin reaction product contains a mixture of oligomers having structuresbelieved to be represented by the following formula III:

[0048] wherein X and Y are the same as in formulae Ia and Ib, a is 0 or1; n is 0 to 5; R² is independently —C(R⁵)₂— or —C(R⁵)₂—O—C(R⁵)₂—,wherein R⁵ is independently hydrogen, alkylol, hydroxyl, alkyl, aryl oraryl ether; and R³ is independently alkylol, alkyl, aryl or aryl ether.Preferably, R² is methylene or oxydimethylene and R³ is methylol. If6,7-dihydroxy-2-naphthalenesulfonate, sodium salt is the modifyingagent, X will be SO₃ ⁻Na⁺ and each Y will be OH. It should be recognizedthat in this case the hydroxy groups for Y will also act as chelatinggroups with a metal ion.

[0049] The autodepositable component can be present in the compositionin any amount that provides for effective autodeposition. In general,the amount can range from 1 to 50, preferably 5 to 20, and morepreferably 7 to 14, weight percent, based on the total amount ofnon-volatile ingredients in the composition.

[0050] The control agent is any material that is able to improve theformation of an autodeposited coating on a metallic surface and,optionally, improve the formation of another autodeposited coatingapplied after the control agent-containing autodeposited coating.Addition of the control agent also increases the uniformity of thethickness of the autodeposited coating. The control agent-containingcomposition does not require an ambient staging period in order todevelop fully the coating. In other words, the metallic coatingconversion is complete upon drying of the coated substrate and anysubsequent coating, primer or adhesive compositions can be appliedimmediately after coating and drying of the control agent-containingcomposition. The control agent also must be compatible with the othercomponents of the composition under acidic conditions withoutprematurely coagulating or destabilizing the composition.

[0051] The control agent may be a nitro compound, a nitroso compound, anoxime compound, a nitrate compound, hydroxyl amine, or a similarmaterial. A mixture of control agents may be used. Organic nitrocompounds are the preferred control agents.

[0052] The organic nitro compound is any material that includes a nitrogroup (—NO₂) bonded to an organic moiety. Preferably, the organic nitrocompound is water soluble or, if water insoluble, capable of beingdispersed in water. Illustrative organic nitro compounds includenitroguanidine; aromatic nitrosulfonates such as nitro ordinitrobenzenesulfonate and the salts thereof such as sodium, potassium,amine or any monovalent metal ion (particularly the sodium salt of3,5-dinitrobenzenesulfonate); Naphthol Yellow S; and picric acid (alsoknown as trinitrophenol). Especially preferred for commercialavailability and regulatory reasons is a mixture of nitroguanidine andsodium nitrobenzenesulfonate.

[0053] The amount of control agent(s) in a multi-component compositionmay vary, particularly depending upon the amount of any acid in thecomposition. Preferably, the amount is up to 20 weight %, morepreferably up to 10 weight %, and most preferably 2 to 5 weight %, basedon the total amount of non-volatile ingredients in the composition.According to a preferred embodiment, the weight ratio of nitroguanidineto sodium nitrobenzenesulfonate should range from 1:10 to 5:1.

[0054] The organic nitro compound typically is mixed into thecomposition in the form of an aqueous solution or dispersion. Forexample, nitroguanidine is a solid at room temperature and is dissolvedin water prior to formulating into the composition.

[0055] The compositions of the invention may be prepared by any methodknown in the art, but are preferably prepared by combining and millingor shaking the ingredients and water in ball-mill, sand-mill, ceramicbead-mill, steel-bead mill, high speed media-mill or the like. It ispreferred to add each component to the mixture in a liquid form such asan aqueous dispersion.

[0056] For the salt chamber test the parts are scored to the metalsurface in a cross hatch pattern using a new razor blade and placed in astandard salt spray chamber for 500 hours. Evaluation of corrosion creepis made.

[0057] Experimental:

[0058] Autodepositable Coating: Component Solids wet wt. % Dry wt. (Lb)Raven ® 14 100 0.43 1.448 owder Marasperse ® 100 0.14 0.472 BBOSO-4Phenolic resin 51 1.42 19.616 Ga. Pacific 4000 ABS latex 50.250 10.417.696 Nitroguanidine 75 0.090 0.227 Deionized 0 77.52 00 water

[0059] Withdrawal Rate for Coating: The small adhesive dip line was usedto vary the withdrawal rate. The following withdrawal rates were used.

[0060] Run 1—7.5 ft/min

[0061] Run 2—5.7 ft/min

[0062] Run 3—3.4 ft/min

[0063] Run 4—1.0 ft/min

[0064] Run 5—Control—Removed manually at 40 ft/min simulating commercialwithdrawal rates.

[0065] Processing of the HRS Panels is as follows: Immersion ProcessStep Chemistry Time Temperature Comments Alkaline Clean Challenge 4minutes 175° F. 8 oz/gal; 1245 w/ ultrasonics Rinse Tap Water 3 minutesRT Air bubbler on Acid Pickle Challenge 5 minutes 130° F. 7% by vol 2527w/ultrasonics Rinse Tap Water 15  80° F. seconds Rinse Tap Water 30 120°F. seconds MJ Metal MJ 1100 30 RT Lot 03221006 Treatment seconds DFTRange 0.19-0.25 mils Dry 7 minutes 220° F. Cool part 4 minutes 120-130°F. MJ Coating MJ 2110 15 RT Lot 03271006 seconds Dry 8 minutes 200° F.B-Stage 20 350° F. Blue-M Oven minutes

[0066] Results: Time elapsed to last Drip Run Number (sec) DFT AVG(STDEV) 1 (7.5 ft/min) 17 sec (One 1.03 (0.156) mils drip) 2 (5.7ft/min) No Drips 1.14 (0.045) mils 3 (3.4 ft/min) No Drips 1.15 (0.054)mils 4 (1.0 ft/min) No Drips 1.20 (0.053) mils 5 (Control) 30 sec ofDrips 1.03 (0.152) mils

What is claimed is:
 1. In an autodeposition coating process for forminga coating on a electrochemically active metal substrate which is dippedin an acidic bath, said coating derived from deposition of a dispersedresin in the bath on interaction of multivalent ions entering theaqueous phase, and wherein said substrate is characterized by no rinsingstep, and a substrate withdrawal rate that is less than the drainagerate.
 2. The process according to claim 1 wherein the electrochemicallyactive metal is selected from zinc, iron, aluminum, cold-rolled steel,polished steel, picked steel, hot-rolled steel and galvanized steel. 3.The process according to claim 1 wherein said substrate is immersed insaid acidic bath for a time of from 20 to 80 seconds before withdrawal.4. The process according to claim 1 wherein said metal substrate istreated with a primer prior to dipping said substrate.
 5. The process ofclaim 1 wherein said dispersed resin is a vinyl-based resin.
 6. Theprocess of claim 1 wherein said resin is a condensation resin.
 7. Theprocess according to claim 1 wherein the coating has an average nominaldry film thickness of from 0.5 to 3 mils (0.0127 mm to 0.076 mm).
 8. Theprocess according to claim 1 wherein said acidic bath has a solidscontent of from 3% to 10%.
 9. The process according to claim 1 whereinthe withdrawal rate is from 1 to 10 ft./min. (30.48 cm. To 25.4 cm.).10. The process according to claim 1 wherein the dry film thickness ofsaid coating has a standard deviation of within 0.05 to 0.16 mils(0.00127 to 004 mm).
 11. The process according to claim 1 wherein saiddispersed resin is based on a polymerizate from monomer selected fromthe group consisting of styrene and butadiene, acrylate,alkyl-substituted acrylate, vinyl halide monomer, vinylidene halidemonomer, alkylene monomer; halide-substituted alkylene monomer andacrylonitrile monomer.
 12. The process according to claim 11 whereinsaid dispersed resin is selected from emulsions or dispersions of(poly)butadiene, neoprene, styrene-butadiene rubber,acrylonitrile-butadiene rubber, halogenated polyolefin, acrylic polymer,urethane polymer, epoxy, polyester, ethylene-propylene copolymer rubber,ethylene-propylene-diene terpolymer rubber, styrene-acrylic copolymer,polyamide, and poly(vinyl acetate).
 13. The process according to claim 1wherein said dispersed resin is a butadiene latex polymerized in thepresence of a compound selected from the group consisting of styrenesulfonic acid, styrene sulfonate, poly(styrene sulfonic acid), orpoly(styrene sulfonate).
 14. The process according to claim 1 whereinsaid bath comprises a modified phenolic resin and a flexibilizer. 15.The process according to claim 4 wherein said primer comprises aphenolic resole, and the coating on said primer comprises a novolak. 16.The process of claim 1 wherein the coating polymer is derived from vinylmonomers selected from the group consisting of acrylic acid, methacrylicacid, acrylic acid esters, methacrylic acid esters, vinyl amides,nitriles, vinyl esters, vinyl ethers, vinyl halides, vinylidene halides,vinyl aromatic compounds, other ethylenically unsaturated compounds andcombinations thereof.
 17. The process of claim 14 wherein saidflexibilizer is selected from (poly)butadiene, neoprene,styrene-butadiene rubber, nitrile rubber, halogenated polyolefin,acrylic polymer, urethane polymer, ethylene-propylene copolymer rubber,ethylene-propylene-diene terpolymer rubber, styrene-acrylic copolymer,polyamide and poly(vinyl acetate).